1 Field of the Invention
The present invention relates to an improved process for the monoethoxylation of phenols whereby fragrance quality ethylene glycol monoaryl ethers, such as ethylene glycol monophenyl ether, are produced.
2. Description of the Prior Art
Ethylene glycol monoaryl ethers are known. These compounds are usually obtained by reacting phenol with ethylene oxide in the presence of an alkaline catalyst. Processes utilizing a variety of basic catalysts such as ammonia, urea, amides, hydroxides and phenates of sodium and lithium, potassium hydroxide and the like are described in U.S. Pat. Nos. 2,852,566; 3,354,227; 3,364,267; 3,525,773; 3,642,911 and 3,644,534.
Whereas products obtained by such processes are suitable for most commercial applications they are not completely acceptable for use in cosmetic preparations and fragrance formulations due to the presence of an objectionable pungent "metallic" odor. Ethylene glycol monophenyl ether obtained by such processes, for example, cannot be utilized in cosmetic preparations or as a solvent and fixative for perfumes without further purification since the undesirable metallic note masks the pleasant odor of the ethylene glycol monophenyl ether and any other fragrance chemicals employed therewith. Even when the ethylene glycol monophenyl ether is carefully distilled after ethoxylation to obtain high purity water-white product essentially free of catalyst residue, unreacted phenol and higher ethylene oxide adducts, the undesirable metallic note is still not completely removed.
In U.S. Pat. No. 4,404,407 a post-treatment procedure whereby ethylene glycol monophenyl ether is contacted with sodium borohydride to eliminate the undesirable metallic note and thus obtain a highly useful fragrance grade ethylene glycol monophenyl ether is disclosed. Treating with sodium borohydride also generally obviates the need for distilling the product.
The post-treatment of polyethoxylated products (having 3 to 80 moles ethylene oxide condensed therewith) with sodium borohydride to improve color is reported in the technical literature of Ventron Corporation Chemicals Division in a brochure entitled "Hydride Chemicals for Process Stream Purification". It is also suggested that another method of treatment of the polyethoxylates would be to add the sodium borohydride with the caustic used as a catalyst for the condensation to prevent the darkening that normally occurs during reaction. A similar procedure is suggested for the production of ethoxylated fatty alcohol surfactants in PROCESS STREAM PURIFICATION NEWSLETTER, December 1979, Issue No. 3, published by Thiokol/Ventron Division. All of the above procedures deal with the treatment or manufacture of polyethoxylates and there is no indication that fragrance quality ethylene glycol monoaryl ethers be obtained by similar methods.